Antenna system having a directionally variable radiation pattern



HOGG ANTENNA SYSTEM HAVING A DIRECTIONALLY June 23, 1959 VARIABLERADIATION PATTERN n 4 Sheets-Sheet 1 Filed April 29, 1955 IN l/ENTOR VATTORNEY June 23, 1959 D. C. HOGG ANTENNA SYSTEM HAVING A DIRECTIONALLYVARIABLE RADIATION PATTERN 4 Sheets-Sheet 2 Filed April 29. 1955 Y m m m.A x

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INI /ENTOR DLIHOGG @zxm ATTORNEY June 23, 1959 Filed April 29, 1955 D.C. HOGG ANTENNA SYSTEM HAVING A DIRECTIQNALLY VARIABLE RADIATION PATTERN4 Sheets-Sheet 3 Repeafer lNl/ENTOR D C. H066 ATTORNEY 4 Sheets-Sheet 4n. c. HOGG A {ANTENNA SYSTEM HAVING A DIRECTIONALLY Filed April 29. 1955June23, 1959 VARIABLE RADIATION PATTERN INVENTORY A QCJ-IOGG ATTORNEYthan m8 I v mokuwmkwm uiomsgzw ni-tfid States Pater SYSTEM- ADIRECTIONALLY VARIABLE RADIATION PATTERN This invention relates todirectional antenna systems for high frequency electromagnetic waveenergy and more particularly to antenna systems for rapid lobe switchingor for simultaneous transmission and/or reception of more than oneelectromagnetic signal in more than one direction.

By far the great majority of directional antenna systems heretoforeemployed in microwave transmission systems depend upon mechanicallymoving structures to effect changes in radiation pattern. Thus, inantenna systems designed primarily for lobing, the rapidity with whichthe lobe switching may occur has been hampered by the speed limitationsof the mechanically moving structures. Other systems for changing thedirectivity of the radiation pattern have utilized an array of manyradiating elements to which energy is fed with varying relative phaserelationships. These systems however are large, complexand "cumbersome;Another system varies directivity of the'radiation pattern by varyingthe frequency of the electromagnetic ener'gy'which transits a refractingmeans whose'index of refraction varies with frequency. This lattersystem sufiers through the requirement of excess bandwith.

It is, therefore, an object of the present invention to accuratelycontrol by electrical means, utilizing minimum bandwith, the radiationpattern of an electromagnetic wave antenna.

It is a further object of the invention to provide an antenna system forangular lobing that is of simple and compact construction andindependent of mechanical motion as a unit or by any of its components.

In the art it is known. that two different information bearing signalsmay be simultaneously transmitted and/ or received between two locationswithout interference or crosstalk as may be the case between twomicrowave relay stations. This may be accomplished in a bandwidth nowider than that required for one information bearing signal bypropagating the signals as orthogonally polarized waves. However, ahighly desirable feature would be to have this type of simultaneousradiation directionally selective.

Therefore, it is an additional object of the invention to electricallycontrol the radiation pattern of a first microwave antenna station toprovide simultaneous transmission and/or reception of informationbearing signals of the same frequency band to and from second and thirdstations separately located.

These and related objects are achieved in the present invention byapplying orthogonally polarized waves to a refracting device whichdeviates the waves by different amounts corresponding to thepolarizations of the waves, thereby controlling the directivity of amicrowave antenna systems radiation pattern. In particular, ananisotropic refractor is employed, i.e., a refractor which exhibits anelectrical path of a particular length to a given portion of a firstwave front polarized in a given direction, while exhibiting a differentlength electrical path to the same portion of a second wave frontpolarized perpen- 2,892,191 Patented June 23, 1959 dicularly to thefirst wave front. Thus orthogonally polarized wavessee diflerent indicesof'refraction in their propagation through the refractor and thus aredeviated from their incident paths. by different amounts.

In accordance with one of the preferred embodiments of the invention tobe hereinafter described in detail, a conventional antenna structure ismodified by the inclusion of an anisotropic refracto r and a device forrotating the electric-field vector orientation of a linearly polarizedwave between vertical. and horizontal. As a consequence a train of wavesalternating in polarization between vertical and horizontal are radiatedfrom the refractor in alternating directions, thus lobing a plane.

In accordance with another of. the preferred embodiments of theinvention also to be described in detail, a conventional antenna systemis modified by the inclusion of the aforementioned anisotropic refractoranda device controlling the polarization of the waves so as tosimultaneously apply orthogonally polarized waves to the refractor. Thisresults in the wave radiating from the refractor in two differentdirections simultaneously; each direction being related to onepolarization. A special feature residing in this'embodiment of the.invention is apparent if the orthogonally polarized waves are thevehicle for respectively diiferent information. The double lobedradiation pattern describes transmission to and/ or reception from twoseparately located stations; the two lobes describing diifeernt pathsand containing: Waves which may bear different information.

These and other objects and features, the nature of. the presentinvention and its advantages, will appear more fully uponconsiderationof the several illustrative em bodime'nts now to be described inconnection with the accompanying drawings in which:

Fig. lis a perspective view of an embodiment of the invention showing anantenna system including a Faraday eflect polarization rotator, aradiating horn and an anisotropic dielectric refractor;

Fig. 2, given by way of illustration, is a schematic presentationshowing the effectof the anisotropic refractor upon a unipolarized wavepropagated through it;

Fig. 3 is a perspective view of an alternative type of polarizationrotator, mechanical in nature, which may be used'in the embodiment ofFig. 1;

Fig. 4 is a perspective view of an alternative forfrn of anisotropicrefractor;

Figs. 5a and 5b are plane views of alternative forms of metallicelements for use in anisotropic refractors;

Fig. 6 is a perspective view of a second embodiment of the inventionshowing a high gain, deflecting type radiating means in conjunction withan anisotropic refractor;

Fig. 7 is a perspective view of a third embodiment of the inventionshowing an antenna system including a selective mode transducer; and

Fig. 8 is a plane view of an application of one aspect of the inventionto microwave relay systems.

In these figures, corresponding parts are indicated by like referencenumerals and characters.

Referring more specifically to Fig. 1, a lobing antenna system is shownas an illustrative embodiment of the present invention comprising theorganization to be described of a conventional horn-type radiatingelement together with a polarization rotator, an anisotropic refractorand the associated terminal equipment therefor. Disposed about acircular wave guide 13 of the metallic shield type, and insulatedtherefrom, is a coil 14 of electrically conductive metal whose terminalsare connected to a variable direct-current voltage source 15 oralternatively to a square Wave generator 15' and which provides amagnetic field parallel to the longitudinal axis of guide 13 and thus tothe direction of wave propagation. Located within guide 13 along itslongitudinal axis, and

within the section'covered by coil element 14, is an elongatedpencil-like ferrite element 16. Elements 13, 14, and 16 together form aFaraday effect polarization rotator. At one end, circular guide 13flares outwardly .toform a conventional-type horn 17. This flared horn,section may be shaped in a truncated, right-conical fashion so as toradiate wave energy in space with a plane wave front.

Offset longitudinally from the end of horn 17 is an anisotropicdielectric prism 18 disposed transversely to the longitudinal axis ofguide 13 and horn 17 so as to intercept wave energy radiated from horn17; the two triangular faces of the prism being in a vertical position,while the rectangular face joining the bases of the triangular faces andthe line joining the vertices are in .a horizontal position. Prism 18comprises a plurality of successive horizontal layers 19 of low-lossdielectric material, such as polyfoam, the bottom face of the bottomlayer being the base face of the prism. Disposed vertically in each ofthe horizontal layers is a multiplicity of straight thin metallic wireelements 20 of high conductivity which may be of material such ascopper, aluminum or silver, arranged in horizontal rows and columns inmatrix fashion; the columns being parallel to the triangular faces ofprism 18 and the longitudinal axis of guide 13, and the rows beingperpendicular thereto. The number of columns does not vary from layer tolayer. The number of rows on the other hand does vary with the layer inwhich they appear; proceeding from the apex to 'the'base of prism 18 thenumber of rows may increase with the increase in area of the layer. Thevertical distance between midpoints of the wire elements 20 in any twoadjacent layers is less than one-quarter wavelength to precludedispersive eifects.

'By way of illustrating a specific application of the antenna system ofFig. 1, it is illustrated as being fed from associated terminalequipment comprising a duplexer, transmitter and receiver. A duplexer 8has three wave guides of the metallic shield type branching from .it. Afirst guide 9 is of rectangular cross section and proportioned so as tosupport the dominant mode, TE and disposed such that the electric-fieldvector of the wave is vertically oriented. A high frequency transmitter10 is coupled to the other end of guide 9 whereby transmitter 10 iscoupled to duplexer 8. A second guide 11, of circular cross section andproportioned so as to support the dominant mode, TE is coupled at oneend to high frequency receiver 12 whereby duplexer 8 and receiver 12 arealso coupled to each other via circular guide 11. A

third guide, which is the hereinbefore mentioned circular guide 13,branches from duplexer 8 whereby vertically polarized waves in the TEmode generated by transmitter 10 will be launched, with appropriateaction by duplexer 8, as vertically polarized TE wave energy in circularguide 13. It may be noted that circular guide 13 and also guide 11 willsupport the TB mode having any radial electric vector orientationincluding the horizontal. Thus TE energy in guide 13 linearly polarizedwith any radial orientation may be launched in guide 11, withappropriate action by duplexer 8, and thence accepted by receiver 12.Full consideration as to the dimensions of circular guides forsupporting various modes is presented in any standard textbook on waveguide transmission, such as Southworth, Principles and Applications ofWaveguide Transmission, 1950.

An understanding of the operation of the illustrative embodiment of Fig.1 may best be obtained by considering the respective functions of theFaraday etfect rotator comprising elements 13, 14, 15 and 16 and theanisotropic refractor 18. Consider first the function and operation ofthe Faraday eifect rotator. Current flowing in coil 14 will create amagnetic field with flux lines parallel to the longitudinal axisof guide13 and consequently parallel to the longitudinal axis of ferrite-element16. Con- 4 sider the case in which the field current is low and thus themagnetic field is weak. A vertically polarized wave E entering guide 13will be propagated through the guide and pass through ferrite 16. Inthis passage the electricfield vector of the wave at different points inspace will remain in a vertical position throughout since the magneticfield is too weak to effect the polarization. With a. high field currentand consequently a strong longitudinal magnetic field, verticallypolarized wave E enters guide 13 and remains vertically polarized untilreaching ferrite 14. At this point, ferrite 14 under the influence ofthe magnetic field commences to affect a rotation upon theelectric-field vector. The rotation continues until the wave exitsferrite 14 when the rotation is arrested and E, has been changed to ahorizontally polarized wave E Thus the function of the Faraday rotatorin this embodiment is to present vertically and horizontally polarizedwaves to born 17 to be radiated in space; which of the two polarizationsappears being controlled by the direct-current voltage source 15 or,alternatively, the square wave generator 15'. The Faraday rotator iswell known in the art; full treatment of its theory and principlesincluding structural considerations is presented in Hogan, The MicrowaveGyrator, Bell System Technical Journal, January 1952. a

The prism 18 is anisotropic in the sense that a linearly polarized waveof one orientation passing through will be deviated at an angledifierent from that of a linearly polarized wave having anotherorientation. Consider Fig. 2, where a linearly polarized wave I isincident upon one face of prism 18 at an angle i to a line Pperpendicular to the face. As the wave front passes into prism 18, thephase velocity of wave I decreases; the change in phase velocitydepending upon the change in dielectric constant exhibited to the waveby the new medium. As a consequence, and in accordance with well knownoptical principles, the wave is refracted downward in the direction ofgreatest density of material. The refractive index then, depends uponthe density distribution in the prism, and the dielectric constantexhibited to the polarized wave. It is clear that had there been noprism, wave I would have continued in a straight line along C. Uponemerging from the opposite face of prism 18, wave I is once againrefracted since the phase velocity increases upon re-entering the airmedium. The angle .of refraction r at the second face of the prism istheangle between the wave R (which is wave I twice refracted) and line Pwhich is perpendicular to the second face and is the path a wave wouldfollow hadit entered the prism along P This angle of refraction isreadily shown, by using Snells law, to be (1) r=arcsin [sin A x/n sini-cos A sin 1'] where r=angle of refraction at the second face A=angleof the prism at the verte n=index of refraction 5 i=angle between I andP From Equation 1 it is clear that changing the index of refraction nwill result in a change in the angle of refraction at the second faceeven though the other prism parameters and the angle of incidence remainconstant. Now the index of refraction does change with a change inpolarization of the Wavepropagated through the prism.

Referring again to Fig. 1, consider a horizontally polarized wave Eincident upon the left face of prism 18. The electric-field vectors of Ethen, are perpendicular to the vertical wire elements 20. Thus aspecific dielectric constant is exhibited to the wave, decreasing thephase velocity accordingly and defining an index of refraction n forhorizontally polarized waves. Since the electricfield vectors and wireelements 20 are substantially orthogonal, the value of 11 as is wellknown, will be close to unity. As a consequence Wave E emergent fromprism 18 will be only slightly refracted. If it were possible to haveevery one of elements 20 perfectly perpendicular to the electric-fieldvector then n would be exactly unity. 1

The vertically polarized wave E on the other hand, is parallel to wireelements 20, and as a consequence a dilterent dielectric constant willbe exhibited by prism 18 thanwas exhibited to horizontal wave E Thephase velocity of E through prism 18 is thus less than was that for Ewhereby vertically polarized wave E, is subject to an index ofrefraction n different from and greater than n Therefore, E and E, willemerge from prism 18 each at different angles B and R respectively,measured in a vertical plane, from the linear extension C of incident E,and E That is, E and E will be deviated by angles B and B respectively.It is convenient to know what change in the angle of refraction will beproduced by the value of n changing from n to n,,. This is determined bydilferentiating Equation 1 with respect to n. The result is i i dn=3drThe following table gives some values of dn for small changes dr: 1

dr (dedn grees) Thus, to produce a change in the angle of refraction of2.5 degrees, it is required that dn=n,,n;,,=.l5; thus n "1.575 andmgr-1.425.

The overall operation of the embodiment of the invention represented inFig. 1 may now be considered. Vertically polarized waves generated bytransmitter 10 and passing through duplexer 8, enter the transmissionline at guide 13 and are propagated past ferrite element 16 as asuccession of alternating vertically and horizontally polarized waves Band E conforming to the square wave variation in the magnetic fieldcreated by coil 14 and direct-current voltage source 15 or square wavegenerator 15'. This train of alternating orthogonally polariz'ed wavesis radiated into space by horn 17 and is then incident upon prism 18.Prism 18, being anisotropic, discriminates between the alternatingwaves, deviating the vertically polarized waves E by an angle B from itsincident direction and deviating the horizontal wave E by an angle BWaves traveling in the opposite direction, that is waves received by theantenna system will, by the converse, pass through prism 18 and enterhorn 17 if the horizontal waves E approach prism 18 at angle B and thevertical waves E at an angle B The received waves may then proceedthrough guide 13 and thence to receiver 12 via duplexer 8. However, thereceived waves need not pass through the Faraday rotator in the reversedirection if a suitable duplexing device or direction discriminatingcoupler is located between ferrite 16 and horn 17 to shunt them toanother guide.

Looking at the overall antenna system represented by the embodiment ofFig. 1, it may be conveniently considered as a transmission path whichis of a greater electrical length for one linear polarization than foranother to which is characterized by the phase velocity differentialthrough prism 18 for the orthogonally polarized waves. Although thewaves in this embodiment of the invention are deviated in the verticaldirection, the direction of deviation is purely a matter of choice. Forexample, a horizontal deviation may be achieved by rotating theanisotropic refractor 18, 90 degrees and also rotating each of theorthogonally polarized waves E, and E by the same amount in the samedirection maintaining their orthogonality. This may be readilyaccomplished by physically rotating prism 18 and by having a 90-degreetwist in rectangular guide 9 or by placing a rotatable l80-degreedifferential phase shifting dielectric vane in guide 13 oriented 45degrees to the vertical. Similarly the waves may be deviated in anyother radial direction by appropriate rotation of prism 18 and theorthogonal waves B and E While the non-mechanical, non-reciprocalFaraday rotator means for providing orthogonally polarized waves isillustrated in Fig. l and is particularly suited for an electricallycontrolled embodiment of the invention, a mechanical, reciprocal devicemay also be utilized. A typical device of this type familiar in the artis the 180- degree differential phase shifter illustrated in Fig. 3.This device, appearing between vertical lines x and y in Fig. 3, may besubstituted for the Faraday rotator appearing between lines x and y inFig. 1. A section of circular wave guide is located longitudinallybetween two stationary circular guides 32 and 33 and is free tomechanically rotate therebetween about its longitudinal axis. Withinthis A ISO-degree section are disposed two thin dielectric fins '34 and35 extending longitudinally along the cylinder, and extending radiallytowards the center, each from diametrically opposite positions on thecross sectional circumference. When the A l80-degree section 31 isrotated such that fins 34 and 35 are disposed 45 degrees to thevertical, the orthogonal components of vertically polarized wave Eentering section 31 from guide 32 will experience a ISO-degreediflerential phase shift during their propagation through section 31. Asa result the vertically polarized entering wave E will emerge fromsection 31 into guide 33 as a horizontally polarized wave E Mechanicallyrotating fins 34- and 35 back 45 degrees to a vertical position resultsin no differential phase shift between the orthogonal components ofvertical wave E and so E will pass through section 31 unchanged inpolarization. This device is theoretically and structurally discussed indetail in South worth, supra. However, since the rapidity with which thedirection of the radiation pattern of the antenna system may oscillateis limited by the rapidity with which the polarization of the wave maybe changed, such a mechanical rotator will primarily be used when slowrates of lobing are contemplated.

The anisotropic refractor took the form of a dielectric prism in theillustrative embodiment of Fig. 1. An equivalent electrical effect maybe obtained by a refractor which need not necessarily conformgeometrically to a prism. Fig. 4 represents an alternative and equallyadequate form. The geometry of this structure is that of a rectangularparallelepiped comprising dielectric layers 19 and straight metallicwire elements 20 disposed and arranged according to the descriptionpreviously presented with respect to prism 18, Le, the number of wireelements per column (or equivalently the number of rows) in eachhorizontal matrix increases in each successive horizontal layer, viewingthe layers from top to bottom. The straight wire elements 20 may bereplaced by other shapes producing somewhat diiferent efiects. Thusalternative shapes may be small rectangles as illustrated in Fig. 5A orellipses as in Fig. 5B. In these cases the refractive index n of ahorizontally polarized Wave (the longer side of the rectangular elementor the major axis of the ellipse being vertical) will not be close tounity as was the case with the straight wire elements 20 since therectangle and ellipse have small components parallel tothe horizontalelectric-field vector. As a consequence these alternative forms willdeviate the horizontal wave by a greater angle than in the case of thestraight elements 20.

Although the refractors described have been of the dielectric type,ferromagnetic refractors may be utilized in a similar manner. Forexample, ferrite material subject to a magnetic field transverse to thepropagation path of electromagnetic waves passing through it willexhibit diflerent permeabilities to orthogonally polarized waves, one ofwhich is parallel to the magnetic flux lines. As a consequence theamount a wave is deviated as a result of its propagation through theferrite will depend upon whether it is parallel or perpendicular to themagnetic field. This type of refractor has a very desirable feature I inthat the permeabilities and thus indices of refraction exhibited to thewaves may be varied very readily by increasing or decreasing theintensity of the magnetic field. Thus, the angle by which the waves aredeviated may be readily varied by varying the magnetic field intensity.The plane in which the angular deviation occurs may be changed by anappropriate and like rotation of the polarization of both the orthogonalwaves, accompanied by a rotation of the magnetic field in the samedirection and by the same amount.

An important application that the embodiment of the inventionrepresented in Fig. l readily lends itself to is in radar systems. Veryrapid small angle lobing of an antenna beam may be achieved since nomechanically moving parts need be involved; the limitation on thefrequency of lobing being the inherent speed limitation of the ferrite16 in rotating the wave polarization (this is of the order of severalkilocycles per second).

Fig. 6 represents a second embodiment of the invention, similar to Fig.1, whereby the Faraday rotator and anisotropic refractor are utilized inan antenna of known high gain properties without substantially effectingany of the design considerations that make it high gain. The radiatingdevice of this embodiment may be of the type disclosed in United StatesPatent 2,416,675, granted March 4, 1947, to A. C. Beck and H. T. Friis.As shown on Fig. 6 this antenna comprises a vertical horn portion 43,having a front wall, back wall and side walls in the form of an invertedsquare pyramidal structure. A parabolic deflector 47 is attached to theback edge of horn 43. Deflector 47 is positioned so as to face both horn43 and the opening 42 which is formed in the plane of the front wall ofhorn 43 by the front edges of shields 40 and 41, of deflector 47. At thelower portion of the antenna a transition section 50 tapers graduallyfrom the square cross section of the throat aperture of horn 43 to thecircular cross section of connecting wave guide 13. A prism 18 of theform hereinbefore described is positioned in front of aperture 42 andparticularly is positioned substantially contiguous to the boundaries ofaperture 42 to cover the aperture. Therefore waves emitted from thethroat of horn 43 are incident upon the concave face of parabolicdeflector 47 and are thereby deflected at a desired angle, maintaining aplane wave front, whence they are then incident upon the face of prism18. Lobing of the radiation pattern then occurs in exactly the samemanner as described with respect to Fig. 1.

Fig. 7 represents an embodiment of the invention for purposes ofillustration, wherein a high frequency selective mode transducerreplaces the Faraday rotator of Fig. 1. As a consequence, not only maythe radiation pattern of the antenna system be lobe switched, but thereceived and/ or transmitted energy pattern may be a simultaneous doublelobe, wherein the lobes diverge in a given plane.

Resulting therefrom, two ditferent signals (information carrying signalsif desired) in the form of orthogonally polarized waves may besimultaneously transmitted to, or received from, two separately locatedsites or stations, or a first signal may be transmitted to a first sitewhile a second signal may be simultaneously received from a second site,in a system of the type hereinafter to be discussed with respect to Fig.8.

The antenna system of Fig. 7 comprises a selective mode transducerending in horn 17 and an anisotropic refracting prism 18. Both horn 17and prism 18 may be of the type hereinbefore described with respect toFig. l and accordingly disposed each to the other. The selective modetransducer comprises two rectangular wave guides 62 and 63 of themetallic shield type electrically coupled to a single circular waveguide 64 also of the metallic shield type. Rectangular guide 62 isdisposed with its widest cross sectional dimension horizontal so thatthe dominant mode transmitted therein, that is the TB has itselectric-field vector oriented vertically. A section of guide 62 isadjacent to, and the vertical wall thereof is contiguous with, a sectionof circular guide 64. Located in this section are several circularapertures 65, such that TE energy from rectangular guide 22 may belaunched in circular guide 64 as TE energy. Rectangular guide 63, on theother hand is disposed with its widest cross sectional dimensionvertical so that although TE energy is also supported therein, theelectric-field vector is horizontally oriented. A section of guide 63 isalso adjacent to circular guide 64, but in this case it is thehorizontal wall that is contiguous thereto and contains couplingapertures 66 for launching TE energy in circular guide 64 as TE energy.Since the wave in guide 63 is horizontally polarized while that of guide62 is vertically polarized, the waves launched simultaneously incircular guides 64 by rectangular guides 62 and 63 will be in the formof cross-polarized TE wave energy. These cross-polarized waves arestable and not undesirably subect to cross-talk between their respectiveinformation carrying signals. One end of circular guide 64 flaresoutwardly to form horn 17 which may be a truncated, right-conical shape.The reverse end of guide 64 is terminated in a reflectionless manner bya termination which is of electrical high loss material. Similarly oneend of guide 62 and guide 63 is also terminated in this manner. Theopposite ends of guides 62 and 63 are respectively coupled totransceivers 61 and 60. The selective mode transducer thus described Wasoriginally disclosed in the copending S. E. Miller application, SerialNo. 245,210, filed September 5, 1951, to which reference may be had fora detailed theoretical and structural analysis and description.

In one mode of operation, orthogonally polarized TE waves aresimultaneously generated by transceivers 61 and 60 and are introducedinto the respective feed ends of rectangular guides 62 and 63. The wavesare propagated through circular guide 64 as cross-polarized 'IE waveenergy. The cross-polarized waves are radiated in space by horn 17 suchthat they are incident upon prism 18. After propagation throughanisotropic prism 18, the cross-polarized waves are deviated from theirincident direction by angles B, and B respectively. Thus the radiationpattern of the antenna system is double lobed with the lobes divergingfrom each other at an angle substantially equal to B minus B measured ina vertical plane. 7

In a second mode of operation, two orthogonally polarized wavessimultaneously propagating through space and approaching anisotropicprism 18 at angles at B and B;, respectively, are refracted through theprism, passing directly into horn 17. Upon reaching the aperturedcouplings 65 and 66 the orthogonal waves are decoupled from circularguide 64 to their respective rectangular guides and thence totransceivers 60 and 61.

In a third mode of operation, a first wave is transmitted from theantenna system at an angle B While ,a second wave, orthogonallypolarized :to the first wave is simultaneously received at an angle B,,,or the converse. There will be little or no interference or cross-talkbetween the two waves since they are orthogonally polarized.

In a fourth mode of operation wave energy is fed alternately to guides62 and 63. The succession of waves emerging from prism 18,alternatingbetween orthogonal polarizations, lobes the vertical plane ina manner substantially similar to that of the embodiment of Fig. 1.Although the angular deviation is vertical in the illustrativeembodiment of Fig. 7, it may be changed to any other planar orientationby appropriate rotation of the anisotropic refractor 18 and theorientation of the orthogonal wave thereto presented, in the mannerpreviously described in connection with Fig. 1.

The selective mode transducer herebefore described is merelyillustrative and any device performing a similar function is appropriatein the antenna system and within the scope of the inventive concept. Forexample, the double polarization feed for horn antennas disclosed in theM. Katzin, United States Patent 2,364,371, issued December 5, 1944, mayadequately be substituted for the selective mode transducer and horn 17.

A cogent application of the embodiment of Fig. 7 in accordance with theinvention, is to microwave relay transmission systems comprising amultiplicity of -repeater stations as illustrated in Fig. 8. A repeaterstation 70, including the embodiment of the invention illustrated inFig. 7, may receive continuous information bearing signals as avertically polarized wave train along propagation path 75 at an angle BRepeater 70 then transmits the information bearing waves as ahorizontally polarized wave train. These waves may be transmittedunrefracted along C to repeater 71', but only if the anisotropicrefractor of repeater 70 is properly designed in the manner discussedabove with respect to Fig. 1. Alternatively, the horizontally polarizedwaves may be transmitted along path 76 at an angle B to line C (C wouldbe the unrefracted path of the horizontal waves). The waves along path76 are thus received at repeater 71 at an angle B Repeater 71 may thenretransmit these waves now vertically polarized, along a propagationpath 77, at an angle B to repeater 72 which is receptive at angle B Theabove operation being continuous, any one repeater simultaneouslytransmits and receives in respectively different directions. Thistransmission, reception and retransmission process may be continued asmany times as required using an appropriate number of repeater stations.If the positions of the repeater stations are fixed because of practicalconsiderations, then the angular orientations of the transmission pathsjoining them define the required indices of refraction of the respectiveanisotropic refractors, thus determining the parameters according towhich the respective refractors must conform. If, on the other hand, theparameters of each refractor are fixed beforehand, the angulargeographic relations of the repeaters, each to the other, areconsequently defined. The fourth mode of operation, above described, ofthe embodiment in Fig. 7 makes the embodiment applicable to a rapidlobing radar antenna system previously explained as one possibleapplication for the embodiment of Fig. 1.

In all cases, it is understood that the abovedescribed arrangements aresimply illustrative of a small number of the many specific embodimentswhich can represent applications of the principles of the invention.Numerous and varied other arrangements can readily be devised inaccordance With these principles by those skilled in the art withoutdeparting from the spirit and scope of the invention.

What is claimed is:

1. A high frequency antenna system comprising means for supportingelectromagnetic wave energy, electrical 10 means for rotating theelectric-field vector of said wave energy, means for radiating waveenergy in space with a plane-wave front, and an anisotropic dielectricprism located in the path of said radiated wave energy, whereby saidprism deviates said wave energy from its predetermined path with amagnitude dependent upon the direction of said electric-field vector ofsaid wave energy.

2. In a high frequency antenna system for linearly polarizedelectromagnetic waves, wave transmission means having differentelectrical path lengths measured in the direction of propagation fordifferent transverse incremental portions of the wave front-of saidwaves, said electrical path length variation defining an index ofrefraction'of said transmission means, said index of refraction of saidtransmission means being variable with electric-field vector orientationof said waves, and means for applying orthogonally polarized wavesalternately to said transmission means, at different points in time,respectively.

3. In a high frequency antenna system for linearly polarizedelectromagnetic waves, wave transmission means having differentelectrical path lengths measured in the direction of propagation fordifferent transverse incremental portions of the wave front of saidwaves, said electrical path length variation defining an index ofrefraction of said transmission means, said index of refraction of saidtransmission means being variable with electric-field vector orientationof said waves, and means for rotating the polarization of said waves tovary the direction of radiation of said antenna system.

4. A combination as set forth in claim 3 wherein said index ofrefraction is substantially unity for a single given electric-fieldvector orientation.

5. In a high frequency antenna system for linearly polarizedelectromagnetic waves, wave transmission means having differentelectrical path lengths measured in the direction of propagation fordifferent transverse incremental portions of the wave front of saidwaves refracting the front of said waves and thereby changing itsdirection of propagation, said transmission means having differentelectrical path lengths measured in the direction of propagation fororthogonally polarized waves, whereby waves of orthogonal polarizationare refracted by diflferent amounts, and means for rotating thepolarization of said waves between said orthogonal polarizations to varythe direction of radiation of said antenna system.

6. A high frequency antenna system comprising means for supportingelectromagnetic waves, means for rotating the electric-field vector ofsaid waves, means for radiating said waves in space, and an anisotropicrefracting means located in the path of said radiated waves, whereby theangle of refraction of said waves through said anisotropic refractingmeans varies with the rotation of said electric-field vector.

7. A combination as set forth in claim 6, and means for controlling saidpolarization rotating means to confine said vector rotation to discrete-degree oscillatory variations, the variation of said vector orientationversus time describing a square wave function.

8. A combination as set forth in claim 6, wherein an elongated ferriteelement is located within said polarization rotating means.

9. A combination as set forth in claim 8, wherein said ferrite elementis subject to a magnetic field whose intensity varies with time as asquare wave.

10. A combination as set forth in claim 6 wherein said electric-fieldvector rotating means comprises at least one thin -degree differentialphase shifting dielectric vane, whereby rotation of said vane about thelongitudinal axis of said supporting means defines a directlyproportional rotation of the electric-field vector of said waves.

11. A combination as set forth in claim 6, wherein said refracting meansis constrained by means maintaining the axes of said refracting means ina constant ,angular position relative to a given direction and sense ofsaid electric-field vector.

12. A combination as set forth in claim 6, wherein said anisotropicrefracting means comprises ferromag netic material subject toa variablemagnetic field.

13. A combination as set forth in claim 6, wherein said radiating meanscomprises an outwardly flaring horn ending in a parabolic deflector,whereby waves propagated through said horn are incident upon saiddeflector and thus radiated in space in other than said incidentdirection.

14. A- combination as set forth in claim 6, wherein said anisotropicrefracting means comprises a dielectric prism.

- 15 A combination as set forth in claim 6, wherein 15 90,1

a source .of electromagnetic wave energy is coupled to said supportingmeans.

, 1 6 A combination as set forth in claim 6, wherein a means forreceiving electromagnetic wave energy is 5 coupled to said supportingmeans. 7

- References Cited in the file of this patent UNITED STATES PATENTS 102,042,302 Frantzet alt May 26, 1936 2,131,042 Halstead V Sept. 27, 19382,311,435, Gerhard Feb. 16, 1943 2,576,146 Ruze et al Nov. 27, 19512,677,056 Cochrane et a1 Apr. 27, 1954 Sichak ,Apr. 23, 1957

